1. Field of the Invention
The present invention relates to improvement in a signal transmitting apparatus of an elevator.
2. Description of the Related Art
The configuration of a conventional signal transmitting apparatus of an elevator is described below with reference to FIG. 4. FIG. 4 is a block diagram of a conventional signal transmitting apparatus of an elevator disclosed in, for example, Japanese Patent Laid-Open No. 1-226685.
In FIG. 4, on a control panel 1 in a machine room are provided a main microcomputer 2 for controlling the movement of an elevator, a hall transmission control microcomputer 3 for controlling serial transmission on the side of halls and a car transmission control microcomputer 4 for controlling serial transmission on the side of a car.
Hell microcomputers 6, 7, 8 and 9 are connected to the hall transmission control microcomputer 3 through a signal line 5. On the Other hand, a car indicator control microcomputer 12 and a car operating panel control microcomputer 13, both of which are provided in a car 11, are connected to the car transmission control microcomputer 4 through a signal line 10. Although the signal lines alone are shown as transmission lines, a power source line, a GND line and the like are also present.
The signal transmission in the above-described conventional apparatus is in an unbalanced half-duplex transmission system. This half-duplex transmission system has problems in that only to a small amount of data is transmitted at a low processing speed because data is transmitted and received through a single signal line. Accordingly, to avoid the preceding problem unbalanced full-duplex transmission systems have been employed.
Another conventional apparatus which uses an unbalanced full-duplex transmission system is described below with reference to FIG. 5.
In FIG. 5, the transmitting section T.sub.x of a hall transmission control microcomputer 3 is connected to the receiving section Rx of each of hall microcomputers 6 to 9 through a signal line 14, and the receiving section Rx of the hall transmission control microcomputer 3 is connected to the transmitting section Tx of each of the hall microcomputers 6 to 9 through a signal line 15. The transmitting section Tx of a car transmission control microcomputer 4 is connected to the receiving section Rx of each of car microcomputers 12 and 13 through a signal line 16, end the receiving section Rx of the car transmission control microcomputer 4 is connected to the transmitting section Tx of each of the car microcomputers 12 and 13 through a signal line 17. Although the signal lines alone are shown as transmission lines, a power source line, a GND line and the like are also laid.
The hall microcomputers 6 to 9 and the car microcomputers 12 and 13 successively transmit data by polling from the hall transmission control microcomputer 3 and the car transmission control microcomputer 4, respectively. However, the number of hall microcomputers to be polled is increased as the number of the hall microcomputers installed is increased, and transmission thus requires a long time. The procedure of transmission is established so that data can be simultaneously transmitted from each of the hall microcomputers 6 to 9 and each of the car microcomputers 12 and 13 to the hall transmission control microcomputer 3 and the car transmission control microcomputer 4, respectively. In addition, a driver of the transmitting section Tx of each of the hall microcomputers 6 to 9 and the car microcomputers 12 and 13 comprises an Open collector type transistor having a hardware (H/W) which allows data collision.
An unbalanced signal transmission line has low noise resistance and is thus difficult to use for long-distance transmission. For example, in the signal transmitting apparatus of an elevator shown in FIG. 5, when a transmission distance is several hundreds m or more, the noise resistance deteriorates, and transmission error is detected.
The case where balanced signal transmission lines are used for increasing the transmission distance is described below with reference to FIG. 6. FIG. 6 shows only the transmission lines through which a hall microcomputer 6 (transmission side) transmits data no a hall transmission control microcomputer 3 (receiving side). A driver 18 on the transmission side 6 is connected to a receiver 22 comprising a differential amplifier on the receiving side 3 through a balanced transmission line 19 comprising signal lines 20 and 21.
For instance, when a high-level signal is output from the transmission side 6, the signal line 20 is a high level, and the signal line 21 is a low level so that the receiving side 3 receives a high-level signal. When a low-level signal is output from the transmission side 6, the signal line 20 is in a low level, and the signal line 21 is in a high level so that the receiving side 3 receives a low-level signal. Namely, Since the receiving side 3 receives data on the basis of a difference between two signal levels, the noise resistance is excellent. Although FIG. 6 shows only the transmission line from the hall microcomputer 6 to the hall transmission control microcomputer 3, the same transmission line is provided for transmission from the hall transmission control microcomputer 3 to the hall microcomputer 6.
A description is now be made of the case where the balanced transmission line shown in FIG. 6 is applied to the elevator signal transmitting apparatus shown in FIG. 5. If the output from all the hall microcomputers 6 to 9 is connected to the signal lines 20, 21 by wired OR, for example, when the hall microcomputer 6 outputs a high-level signal, and when the hall microcomputer 7 outputs a low-level signal, the driver 18 of the hall microcomputer 6 drives the signal line 20 in a high level and the signal line 21 in a low level, and the driver 18 of the hall microcomputer 7 drives the signal line 20 in a low level and the signal line 21 in a high level. As a result, both signals collide with each other, and the output of the receiver 22 becomes unstable. Namely, collision of data is not allowed.
Thus the balanced transmission lines must be laid in one-to-one correspondence between the hall transmission control microcomputer 3 and the hall microcomputers 6 to 9. This increases the number of signal lines required and thus causes an increase in the cost and deterioration in the workability.
The above-described conventional elevator signal transmitting apparatuses have the problem that long-distance transmission cannot be easily achieved by unbalanced transmission lines alone from the viewpoint of noise resistance.
The conventional apparatuses also have the problem that since wired OR connection cannot be made by balanced transmission lines alone, the number of signal lines increases, the interface cost increases, and the transmission efficiency deteriorates.